Controlling the chemistry of small drops is troublesome owing to the difficulty in handling and metering small volumes. To change the chemistry of a 50 nl drop by 10% would require adding or removing a 5 nl quantity—a very difficult proposition. Most nanovolume assays are set up once and never modified afterwards.
Large environmental systems have been built to provide vapor controlled change of chemistry. However, these are far too bulky and inconvenient to be of use to a typical researcher and have seldom been used in nanovolume assays.
Thus, it would be desirable to provide a simple method and apparatus for vapor controlled change of the chemical compositions of small droplets.